Volume 57 Number 6 Date 05/17/2012
WEEDS IN CORN - Most corn fields in the south-central and southwest counties are in the V1-V2 stage of growth. Now is an important time to identify the predominant weed species present in fields and plan controls accordingly. Factors influencing corn's competitiveness at this early stage vary based on row spacing, available nitrogen, moisture levels and weed composition. To prevent early yield losses, all fields should be evaluated for site-specific weed problems. Corn is most susceptible to yield loss from weed competition during the V3-V8 stages and should be kept as weed-free as possible during this period.
VELVETLEAF - Planting operations have triggered velvetleaf emergence in southern Wisconsin corn fields. Small plants ranging 2-3 inches in height were observed in Dane, Rock and Walworth counties this week. A velvetleaf infestation of only three plants per foot of row has been shown to cause yield losses of 20% or more. Monitoring potential problem areas in corn fields is recommended through the eight-leaf stage (V8).
WINTER ANNUALS - Dense populations of winter annual weed species such as chickweed, field pennycress, shepherd's purse, speedwell and yellow rocket are common in unplanted no-tillage fields. Presumably, many of these fields will be planted to soybeans in the coming weeks. With winter annuals at advanced stages of growth, it is critical to apply a burndown herbicide prior to or shortly after planting. Delaying control until soybeans are in the VC-V1 growth stage can result in yield reductions of 8-9 bu/acre.
--Clarissa Hammond, DATCP Weed Scientist